This amp is just a more powerful brother of the above. The output
transistors are not darlingtons anymore.
The bias
current is 55 mA. The output coil is 16 turns of 1.5mm wire on
an 8mm diameter.
The best visible difference is seen in the
input stage - the differential amp has 5 transistors in each branch
instead of three. The two additional transistors, T7+T8 / T9+T10, take
over the voltage, while the rest is responsible for the amplification. The
T1 to T6 don't have to carry the high voltage and can be low-noise types,
while T7 to T10 carry the voltage.
The author says there's another
important advantage - this solution subdues Miller's feedback CB
capacities of the differential amplifiers which improves slew rate and
thus distortion on high frequencies.
Also the transistors of the
differential amplifier work at a constant voltage which improves
linearity and th us contributes to lower distortion.
The
trafo should be about 2*40 Volts and 12 to 15 Amps.
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